Adjunctive application of solid‐state culture products and its freeze‐dried powder from Aspergillus sojae for semi‐hard cheese

Abstract

BACKGROUND Species belonging to the genus Aspergillus have been used in traditional Japanese fermented foods. Aspergillus sojae is a species responsible for strong proteolytic activity. Freeze‐drying treatments followed by physical disruption enables the pulverization of the mycelia of A. sojae RIB 1045 grown in whey protein‐base solid media. Intracellular proteases were extracted using this protocol to compare extracellular protease activity in terms of the reaction’s pH dependence in the presence or absence of inhibitors. RESULT With different sensitivities to inhibitors, intracellular and extracellular proteases showed the strongest activity under acidic conditions, which were considered suitable for cheese application. The raw culture product (CP) and its freeze‐dried product (FDP) were mixed with cheese curds, prepared according to Gouda‐type cheese‐making methods, and were allowed to ripen for 3 months. Chemical analysis of the products showed 13.3% water‐soluble nitrogen (WSN) in the control, which had received noncultured media, whereas 20.0% and 21.1% WSN was found in the CP and FDP experimental cheeses, respectively. Although these adjuncts significantly increased WSN, an insignificant difference was found between CP and FDP. Free fatty acids in all experimental cheeses were similar, showing that CP and FDP caused no rancid defects. CONCLUSION The introduction of freeze‐drying treatments accompanied by cell disruption resulted in a negligible effect in terms of WSN. However, the application of A. sojae can be beneficial when it comes to increasing the level of WSN compared with A. oryzae, as shown in our previous study. © 2020 Society of Chemical Industry

A study of lipolysis induced by adjuncts from edible Aspergillus sp. solid culture products on ripened semi‐hard cheese

“…Proteolytic activity was determined as previously described, with some modifications 12 . The enzyme reaction was incubated at 30 °C for 1 h. Enzyme activity was expressed as micromoles of released tyrosine per hour at 30 °C extracted from 1 g of the CPs (1 μmol tyrosine h −1 g −1 CP = 1 protease unit: PU).…”

“…Cheesemaking was carried out according to the conventional procedure for Gouda‐type cheese, as previously described 12 . Raw milk was obtained from the experimental farm in the Field Science Center for Northern Biosphere, Hokkaido University, and 105 kg standardized milk (3% fat) was used in this study.…”

“…Moisture, fat, protein and water‐soluble nitrogen (WSN) were determined as previously described 12 . For FFA determination, the cheese sample (0.2 g) was transferred to 2 mL of 7.7 mol L −1 HCl in a test tube and placed in boiling water to dissolve the sample.…”

“…The strains used in this study were as follows: A. kawachii NBRC 4308, from Biological Resource Center (Chiba, Japan); A. luchuensis RIB 2604, kindly gifted by the National Research Institute of Brewing (Hiroshima, Japan); and A. oryzae AHU 7139, from the culture collection of Hokkaido University. The spore suspension was prepared as described in previous study, 12 to a concentration of 2.5 × 10 5 spores mL −1 .…”

“…Since a remarkable increase of FFA in the cheese was recognized with the adjunct of A. oryzae , its cause was investigated from the viewpoint of the retainability of lipases on the curds with a simulated experiment to measure the soluble lipase activity before and after incubation with the curds. Furthermore, as the prepared adjunct material was proven to include both extracellular and intracellular lipases, 12 fractionation of the lipases from A. oryzae adjunct materials was carried out to specify the fraction responsible for the FFA increase in A. oryzae cheese. Finally, we proposed a possible mechanism of FFA accumulation during cheese ripening that would take place when the adjunct materials from A. oryzae were supplemented.…”